When a ruthless hitman is shot by one of his targets, he is left in limbo. He soon finds out to release his spirit he will have to shoot his own son.

In order to escape limbo after he is killed, a ruthless hitman must murder his own son.

I'm confused ... and this may or may not have anything to do with the quality of the logline, but how could he kill someone if he's stuck in limbo? Wouldn't the mere set up mean that he can leave limbo and return to reality at will? Also, who made this rule that by killing his own son, would he be allowed to pass over into the afterlife?

32 words here - the trick is to try and stick to 25 or less... Very difficult.

The story sounds strong. I think you can cut 'left in limbo'.

Here's an offering:

When a ruthless hitman is shot by one of his targets he faces a terrible dilemma...to release his spirit he must kill his own son....